Manufacture of mirrors



Patented Aug. 24, 1943 MANUFACTURE OF MIRRORS Andrew Levaggi, Dubuque, Iowa No Drawing. Application September 7, 1940,

Serial No. 355,815

3 Claims.

The present invention relates generally to the manufacture of glass mirrors and more particularly to the deposition and treatment of the refleeting metal film on the glass or other hyaline surface so as to form a mirror or reflecting surface. While the present invention is more particularly described herein as applied to the deposition of silver for the formation of a reflecting metallic silver film on the surface of a hyaline body, such as glass, it will be obvious to persons skilled in the art that the present invention may also be applied in the formation of other types of mirrors in which other metals or metallic compounds are deposited as reflecting surfaces, such as gold, copper, lead or the like.

Mirrors are produced sometimes at a stationary bench and at other times conveyor belts are employed. In either case the stationary table as well as themovable conveyor belt are more or less conventionally heated from below by means of steam carrying pipes. The hot pipes radiate their heat to the lower surface of the table top 01' to the lower face of the conveyor belt, these in turn transmitting their heat to the lower face of the glass, the glass then transmitting its heat to the surfac which is being silvered or mirrored and to the solution and preparations which are deposited upon such surface in the process of silvering or mirroring.

One of the objects of the present invention is to supply heat directly to the mirroring solution or preparation in whatever form after the same has been applied to the glass surface where the reflecting metal surface is to be deposited.

Another object of the present invention is to employ electrically generated heat, the source of such heat being so disposed with reference to the surface to be mirrored that its heat is radiated directly to such surface and directly to the mirroring preparation which is employed in the formation of the mirrored surface.

The present invention also aims to employ in the deposition and treatment of the reflecting surfaces a source of heat which provides radiations falling within a. selected range of wave lengths which penetrate into the mirroring and silvering solution so that such heat and radiations are available directly at the surface where the final metallic particles are being formed and deposited upon the glass.

More particularly the present invention aims to employ in the mirroring process a controllable source of radiation a substantial proportion of which is in the near visible infrared range or within the range of 'wave lengths between 10,000 and 16,000 angstrom units or from 1.00 to 1.6 microns,

The useful range, however, includes radiations from .6 to 1.6 microns.

A variety of types of infrared ray electric lamps are now available on the market which may be employed in the present process. Both carbon filament lamps and tungsten filament lamps are available on the market and which produce heat radiations with a very large proportion falling in the near visible infrared range. Either of these types of lamps, each being provided with its own reflector, preferably a gold plated reflector, may be employed in carrying out the present invention. Such, lamps. are preferably mounted in closely spaced banks, th width of the bank being approximately equal to the width of the table or conveyor, and the length of the bank being equal to the length of the table where a fixed table is employed. When the present invention is practiced on a fixed table such bank of lamps is preferably arranged so that it may be raised and lowered, thus providing for free access to the table for the performance of certain operations such as the pouring of the mirroring solution thereon and other manipulations. The bank of lamps may be lowered to within a few inches of the level of the table so that if desired the work. may be subjected to the maximum radiation. When desired, however, the bank of lamps may be raised to any suitable height so as to somewhat reduce the intensity of the radiation. The reflectors are preferably so designed that the, rays admitted by the bulbs are projected downwardly with a slight or suitable spread so that th distribution of the light, or particularly thedistribution of the infra- I red rays, may approximate uniformity at the level of the work. In order, however, further to overcome the possibility of a greater concentration of heat and energy on some portions of the work than on others, the bank of lamps may be oscillated by any suitable means.

I In the application of the present invention to the stationary method mirror manufacture, the bank of infrared ray lamps is first lowered so as to heat the surface of the table. The bank of lamps is then raised and the sheets of glass are then placed on the table with their sensitized faces uppermost. It will be understood that this sensitizing of the surface to be covered with the reflecting metal film is effected in the usual manner well known by those skilled in the art, generally by applying over such surface a sensitizing solution of stannous chloride, the excess of which is rinsed from the surface preliminarily to pouring the reflecting metal solution thereon. The

bank of lamps is then again lowered so as to heat the exposed surfaces of the glass plates. The bank of lamps is then again raised and the silvering solution is poured onto the glass plates. The bank of lamps is now lowered to the desired height so that the infrared radiations serve to heat the solution as well as the glass immediately below the solution and by penetrating the solution such radiations are available throughout the body of the solution where the chemical reaction is proceeding and at the very surface where the fine metal particles are being deposited for the formation of the reflecting film. Although it may be preferable in certain instances to initially heat the table prior to placing thereon the glass or other hyaline body to 'be silvered. this is not essential to the successful practice of the process of the present invention inasmuch as quite satisfactory results may be obtained by placing theglass on a cold or unheated table, then pouring the silvering solution thereon and finally subjecting, from above, the solution-covered surface to the activating and heating influence of the infrared radiation derived from a controllable source, such as the infrared ray lamps. Obviously, however, a somewhat longer time would be required to precipitate the silver where the table is not pre-heated.

If desired, the subsequent drying operation as well as the drying of the protective coating may also be accomplished by the use of the bank of infrared ray lamps, but such drying operation per se forms no part of the present invention and is not claimed as such.

When the present process is applied to the conveyor method, the banks of lamps may, if desired, be fixedly mounted, for in the conveyor method any manipulations or any operations that need to be performed on th work are performed at such portions of the conveyor where it is free of obstructions and where there ar no lamps, the lamps being disposed over such portions of the conveyor where the work has to be exposed to heat. When it is desired to vary the intensity of the radiations, such variations may be accomplished by varying the current in the bank of lamps. However, the bank may be so constructed that it may be raised oriowered within certain li-mitations so as to provide this additional method of varying the intensity of radiations to which the work is subjected. In the conveyor method several banks of infrared ray lamps are employed. The first bank, which may be relatively small in number of lamps, is disposed at the loading end of the conveyor belt and-is designed for the purpose of preheating the belt before the glass plates are deposited on the belt. This bank may contain a relatively small number of lamps and may be disposed directly over the belt and perhaps spaced only an inch or two from it. As in the case of the stationary table, preheating of the conveyor belt preliminarily to placing the glass plate thereon may be dispensed with, if desired.

When the sensitized glass plates are deposited on this conveyor belt, which latter may or may not have been pre-heated, the silvering solution is poured over the entire surface of the glass plates. Asthe belt with the glass plates carrying the silvering solution travels, it enters underneath a relatively long and large bank of infrared ray lamps. The length and strength of such lamps will depend in part upon the rate of travel of the belt and in part upon the nature of the work being performed. With a given installation the heat and radiation generated by the lamps may be varied by varying the electric current flowing through the lamps. Such bank may also be madeadiustable vertically for the purpose of providing another method of varying the 1iieat and activating radiation applied to the wor After the silver or other metal has precipitated and the mirrored surface is properly formed. the plate is rinsed with water and again travels under a bank of infrared ray lamps in order to dry all of the moisture from the surface of the silver film preparatory to receiving the proteci'fiiiv'e coatings that are used to cover the silver It will thus be seen that by means of the present invention, the method of manufacturing mirrors is greatly simplified and the variation in treatment of several types of minors is facilitated. In addition, however, it is found that by the present method, namely, by directing infrared radiations onto and into the silvering solution in which the chemical reaction is proceeding with the incident formation of the metallic film, a greatly improved film is obtained and the proportion of defective mirrors obtained is greatly reduced. It is found also that by means of this process the output of any particular installation may be increased. Results obtained by the present process may be due to the fact that the silvering solution as well as the metallic film in the process of formation are both subjected to uniform conditions throughout the process and may also be due in part to the favorable influence of the radiations upon both the chemical and physical processes involved.

The present method is applicable to all types of silvering or gilding solutions as well as to other solutions which yield metallic or reflecting film deposits through chemical reaction. Thus, it may be applied to-silverin'g solutions of silver ammonium nitrate mixed with suitable reducing agents. It may also be applied to silvering solutions which contain some copper salts and which form a silver film containing a small percentage of copper, as well as to other solutions for depositing metallic reflecting films upon glass or other such hyaline bodies. Whichever silvermg or gilding solution is employed, the present process improves the homogeneity, strength and firmness of the metal film and, if desired, may

glsno be employed to increase the thickness of the tion-covered surface of the glass. This time,

however, may vary considerably depending upon variations in the strength of the infrared radiations, in the solution formulae employed and in the proximity of the lamps to the surface to be silvered. Upon employing customary silvering solutions in conjunction with customary reducing agents, I have found that satisfactory precipitation of the silver has been effected in certain instances within a period of as little as live and thicknesses of glass mirrors.

I claim:

1. The process of silver coating glass to form a mirror which comprises coating the surface of the glass with a silver depositing solution, applying by radiation infrared rays from an electric lamp source directly against the surface of said solution for a period of from about five and onehalf to seven and one-half minutes, and controlling the intensity and duration of the rays by positioning the source thereof so that continued penetration of the rays to the depth of the solution is effected during their period of application.

2. The process of silver coating a hyaline body to form a mirrored surface which comprises coating the surface of the body with a silver depositing solution, applying by radiation infrared rays from an adjustable and controllable artificial source directly against the surface of said solution for a period until the body is coated with silver, and controlling the intensity and duration of the rays by positioning the source thereof so that continued penetration of the rays to the depth of the solution is effected during their period of application.

3. The process of coating a hyaline body to form a mirrored surface which comprises coating the surface of the body with a solution of a metal salt and a reducing agent, said metal salt being selected from the group consisting of silver, copper, gold and lead salts, applying by radiation infrared rays from an adjustable and controllable artificial source directly against the surface of said solution for a period until th hyaline body is coated with a reflecting film of the metal deposited out of said solution, and controlling the intensity and duration of the rays by positioning the source thereof so that continued penetration of the rays to the depth of the solution 25 is effected during their period of application.

ANDREW LEVAGGI. 

